The filters are selected so that the mean wavelengths of response functions are 364 nm for U, 442 nm for B, 540 nm for V. The zero point of the B−V and U−B color indices was defined to be zero for A0 V stars not affected by interstellar reddening.

The UBV system has some disadvantages. The short wavelength cutoff of the U filter is defined mainly by the terrestrial atmosphere rather than the filter itself. Thus, it (and observed magnitudes) can vary with altitude and atmospheric conditions. However, a large number of measurements have been made in this system, including many of the bright stars.[2]